The half integer resonance is often used to define the
high intensity limit of medium or low energy hadron rings
where transverse space charge is significant. However, the
mechanism leading to particle loss as beam approaches this
resonance, which thus defines the limit, is not clearly understood.
In this paper we explore simple models, based on
single particle resonance ideas, to see if they describe useful
aspects of motion as observed in simulations and experiments
of 2D coasting beams on the ISIS synchrotron. Single
particle behaviour is compared to 2D self-consistent models
to assess when coherent motion begins to affect the single
particle motion, and understand the relevance of coherent
and incoherent resonance. Whilst the general problem of
2D resonant loss, with non-stationary distributions and nonlinear
fields is potentially extremely complicated, here we
suggest that for a well-designed machine (where higher order
pathological loss effects are avoided) a relatively simple
model may give valuable insights into beam behaviour and
control.